Seven to nine species: tropical Asia and Oceania; two species in China.

Knoxia was revised by Bhattacharjee and Deb (J. Econ. Taxon. Bot. 6(1): 73-96. 1985), who recognized seven species. Then, it was reviewed anecdotally by Puff and Robbrecht (Bot. Jahrb. Syst. 110: 511-558. 1989), who circumscribed it differently and included nine species. The treatment by W. C. Ko (in FRPS 71(2): 3-7. 1999) differed markedly from these others; it did not cite these authors so presumably Ko had not seen their works. In particular, these other authors considered K. sumatrensis to be a wide-ranging, morphologically variable species and included as synonyms of var. sumatrensis two species that were separated by Ko, K. corymbosa and K. mollis. Because it was based on geographically broader studies of more literature and many more specimens from the type regions, Puff and Robbrecht’s taxonomy is used here.

W. C. Ko (loc. cit.: 4) described the fruit as capsules and the seeds as having a thick stipe, but the fruit of Knoxia have more often been described within Rubiaceae as schizocarps with carpophores, as noted here.